Semiconductor devices are known in which semiconductor elements are accommodated in a wiring substrate. For example, the wiring substrate is configured such that plural conductive layers and plural insulating layers are laid alternately on a silicon substrate body and adjoining conductive layers are connected to each other by via holes that penetrate through the insulating layer sandwiched between the adjoining conductive layers. Example materials of the substrate body other than silicon are a metal and a resin. An insulative substrate which is formed with a number of through-holes filled with a metal material may also be used.
Generally, in such semiconductor devices, no heat dissipation path from the back surface of each semiconductor element is provided (for example, see JP-2011-023626-A). Thus, a heat sink or a spreader may be bonded to the back surface of each semiconductor element.
However, in the structure having no heat dissipation path from the back surface of each semiconductor element, it is difficult to keep the element temperature of each semiconductor element lower than a required temperature. On the other hand, a provision of a heat sink or a spreader to the back surface of each semiconductor element lowers the mounting density when semiconductor elements (and other semiconductor devices) are mounted in the semiconductor device.